The subject invention is concerned with the treatment of organic and inorganic waste streams and more particularly to an improved process of operating a system and reactor for treating organic and inorganic wastes.
Municipalities, industry and commercial users have attempted many methods of treating waste streams (i.e. activated sludge, tapered aeration, modified aeration, contact stabilization, step aeration, etc.). However, these systems have not been very efficient in operation, particularly in the operation of the reactor. Difficulty is experienced in effecting and controlling the oxygen transfer from the gas phase to the liquid phase in a reactor and in supplying sufficient oxygen to the system for effective operation.
The prior art in systems treating organic and inorganic wastes generally consist of primary treatment followed by secondary treatment. In very general terms, the primary treatment of waste is a separation of solid settling particles from the liquid phase; secondary treatment consists of taking the primary effluent or the liquid phase of the waste and feeding it to a reactor where the liquid phase (consisting of organic and inorganic waste material) is combined with microorganisms, "activated sludge", into which air or oxygen is injected or diffused to promote the microorganism activity, the biomass is then fed from the reactor to a clarifier where a separation of supernate or clarified liquid is made from the settled activated sludge. The settled activated sludge containing microorganisms is then recycled to the reactor and combined with the incoming primary effluent.
The improvement of the present invention consists of placing a membrane in the reactor between the gas phase and the liquid phase or biomass. The membrane is selected to control the flow of nitrogen and oxygen from the gas phase to the liquid phase or biomass and to control the flow of carbon dioxide from the biomass to the gas phase. By controlling the flow of oxygen and nitrogen through the membrane, an altered or desired atmosphere is established with an increased level of oxygen in contact with the liquid phase thereby permitting increased biological activity and a higher treatment efficiency (i.e., biochemical oxygen demand removal) in the reactor is obtained.
Some of the prior art attempts at introducing oxygen to the liquid phase or utilizing membranes in the treatment system are discussed below.
A type of reactor apparatus is disclosed in U.S. Pat. No. 3,734,850 which is of a general form showing the injection of an oxygen-containing gas to wastewater for aerating the water.
The process and apparatus disclosed in U.S. Pat. No. 3,580,840 is generally directed to the use of a membrane for effecting the separation of contaminated water from the microorganisms. The membrane prevents the microorganisms from passing into the contaminated water while allowing one or more contaminates to be consumed in the microbial metabolism or growth process. Another use of a membrane is shown in U.S. Pat. No. 3,490,590 wherein a selectively permeable membrane is used for separation of liquid carried particles from the liquid.
Another type of process is described in U.S. Pat. Nos. 3,725,258 and 3,547,812 which generally utilize a supply of expensive oxygen rich gas to the reactor in order to increase the biological activity.
Briefly, the present invention is directed to an improved reactor for use in the treatment of organic and inorganic wastes wherein a semipermeable membrane is placed in the reactor between the liquid and gas phase, said membrane being selected to control the flow of oxygen and nitrogen from the gas phase to the liquid phase in a ratio of oxygen to nitrogen greater than 1:4. The membrane also controls the flow of carbon dioxide from the liquid phase to the gas phase. Another aspect of the present invention, is the process of operating a waste treatment system for organic and inorganic wastes wherein the flow of oxygen from the gas phase is controlled to the liquid phase or biomass in a reactor by passage through a membrane between the liquid and gas phase in the reactor. The process will also control the flow of nitrogen from the gas phase to the liquid phase and the flow of carbon dioxide from the liquid phase to the gas phase.